Failures of feedback: rush hour along the highway to obesity.

From hot dogs to Hashimoto's and inheritance to inactivity, many "entrance ramps" converge onto the "Highway to Obesity", each contributing caloric intake that exceeds expenditure. Initially, the hypothalamus regulates appetite and energy based on leptin feedback, until feedback failure increases appetite, and allows deposition of abdominal fat, metabolic dysregulation, and metabolic syndrome. Without feedback controls, progress toward obesity is unimpeded unless diet, exercise, and/or medications provide an exit ramp.

Beyond obesity: the diagnosis and pathophysiology of metabolic syndrome.

Metabolic syndrome (MSX) identifies clinical symptoms and lab results, including abdominal obesity, insulin resistance, hyperglycemia, hyperlipidemia, and hypertension, that lead to an increased risk of cardiovascular disease (CVD). Obesity typically results in insulin and leptin resistance and a shift from expansion of subcutaneous fat to deposition of abdominal and ectopic fat. These conditions cause metabolic dysregulation, elevated fatty acids (FFA), and increased secretion of pro-inflammatory "adipokines". Left untreated, these conditions cause lipotoxicity, chronic inflammation, hypertension, atherosclerosis, and CVD.

A brief survey of aquaporins and their implications for renal physiology.

Aquaporins (AQPs) are an important family of proteins that efficiently channel water through the cell membranes. Although water can diffuse across biological membranes at measurable rates, physiologists had long predicted the existence of channels to facilitate rapid reabsorption of water by renal tubular cells. With AQPs present, water can "gush" through the membrane at the extraordinary rate of three billion water molecules per second per aquaporin channel. In their absence, water only trickles across the hydrophobic lipid bilayers of cell membranes. Aquaporins have fascinated researchers over the last decade, culminating in the 2003 Nobel Prize for Chemistry given to their discoverer, Dr. Peter Agre. During the 1990s, scientists identified and characterized members of the mammalian aquaporin family, now designated as AQP0 through AQP10. AQPs are also found in many plant and bacterial species. However, their relevance to the clinical laboratory is only recently emerging. Dr. Agre's Nobel symposium address provides an excellent mini-review of aquaporins in medicine. Our understanding of renal physiology and pathophysiology has advanced greatly as we account for the subtle implications of various AQP systems. For example, nephrogenic diabetes insipidus (NDI), the inability to produce concentrated urine, can result from several different malfunctions in the AQP2 system controlled by anti-diuretic hormone (ADH). Virtually all mammalian cells incorporate aquaporins into their cell membranes, and many cells produce multiple aquaporins, each with a specific function. It is therefore not surprising that malfunctions have important clinical conditions. The present article discusses the implications of aquaporins for renal physiology, while the accompanying article is focused on the clinical aspects of aquaporins.

CLS meets the aquaporin family: clinical cases involving aquaporin systems.

Virtually all human cells incorporate aquaporins, or water channel proteins, into their cell membrane. Indeed, many cells produce several aquaporins, each adapted for a specific physiologic function. Thus, it is not surprising that aquaporin malfunctions are associated with numerous important clinical conditions. This article describes the clinical aspects of malfunctions in aquaporins or their regulation. Although water can diffuse across biological membranes (osmosis) without the aid of a transport system, researchers had predicted for decades that rapid reabsorption by renal tubule cells must be aided by a channel or pore. Yet, not until the 1990s were the first members of the aquaporin (AQP) family identified. Led by Dr. Peter Agre, recipient of the 2003 Nobel Prize in Chemistry, researchers have since amassed an astounding amount of information about AQPs and their function. For example, the flow rate of water through AQP1 is an extraordinary three billion water molecules per second per aquaporin channel, while a relative trickle of water crosses the hydrophobic lipid bilayer of cell membranes devoid of AQPs. Our understanding of renal physiology and pathophysiology has advanced greatly as we account for the subtle implications of various AQP systems. For example, nephrogenic diabetes insipidus (NDI), the inability to produce concentrated urine, can result from several different malfunctions in the hormonally controlled AQP2 system. The list of diseases known to involve AQPs now includes: early onset of cataracts, Sjogren's syndrome, cerebral and pulmonary edemas, cirrhotic liver development of ascites, and congestive heart failure (CHF).

The emerging roles of BNP and accelerated cardiac protocols in emergency laboratory medicine.

BACKGROUND: The role of the clinical laboratory in emergency cardiac medicine is rapidly evolving; with recent redefinitions of acute myocardial infarction (AMI) and unstable angina (UA) based on troponin levels, recommended acceleration of cardiac testing protocols, and increased clinical measurement of B-type natriuretic peptide (BNP). We briefly review the background pathophysiology of acute coronary syndromes (ACS) and congestive heart failure (CHF), along with an overview of the biochemistry and physiology of the natriuretic peptides. METHODS: The assay principles and performance characteristics of the rapid BNP assays are discussed. The performance characteristics of troponin assays are at the center of controversy regarding the redefinition of AMI and UA, and will be discussed. RESULTS: We review the rapidly expanding evidence regarding the clinical utility of BNP for CHF patients. While BNP has gained wide acceptance as a rapid diagnostic tool, considerable controversy remains concerning its potential for prognosis, screening, and therapeutic monitoring. Although a thorough discussion of the use of cardiac markers is well beyond the scope of this review, overviews of the redefinitions of AMI and UA, and the trend toward accelerated testing protocols to obtain a quicker diagnosis or ruling-out of AMI are included. In addition to accelerating the retesting of existing markers, a recent test for ischemia modified albumin (IMA) promises another quantum leap in cardiac diagnoses. CONCLUSIONS: The positive impact of these developments on the healthcare costs and overall improvement in the quality of healthcare delivery will be discussed. A brief analysis of the downstream costs of BNP testing is also offered.

Mycology at a distance.

GermWare Mycology is an image-rich, CD-ROM-based instruction divided into tutorial and reference programs. The tutorial program, designed for new students, provides only for sequential progress through each of the subject modules, so that each page of information is seen. In contrast, the reference program allows the more experienced learner with random and direct access to each facet of information. The aspergilli, the agents of chromomycosis, the dermatophytes, the dimorphic fungi, the hyaline molds, the dematiaceous molds, the yeasts, and the zygomyces are divided into separate modules. The tutorial program also includes an opening 'isolation procedures' module, in which details of specimen collection, culture media, and microscopic techniques are presented. The random access program includes system maps separating out each of the fungal species, and flow diagrams allowing an algorithm approach to species identifications. A global map is also included through which each fungal species can be directly accessed by the simple click of the mouse. Random access to information on the ecology, clinical presentations, pathology and therapy of the various mycotic diseases is also a feature of the reference program. A series of self-assessment exercises is included at the end of each module, with immediate 'pop-up' feedback to both correct and incorrect answers. The entire program includes over 2500 screens and over 700 color images and diagrams. GermWare Mycology is available through the Colorado Association for Continuing Medical Laboratory Education (CACMLE), who also can provide continuing education credits for individuals who complete a separate examination. For more information contact CACMLE at (303) 321-1734 or info@cacmle.org.